GTA
Airguns by Make and Model => Gamo Airguns => Topic started by: nateious on August 04, 2011, 08:44:35 PM
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About a month ago I noticed something was wrong with my CFX. I could see the pellets flying through the air in the scope where previously I could not. I got out my chrony and the pellets were clocking in about 600fps. When I originaly got the chrony they were doing about 850. I had put up a post about it here http://www.gatewaytoairguns.org/GTA/index.php/topic,15144.0.html (http://www.gatewaytoairguns.org/GTA/index.php/topic,15144.0.html) I built a compressor and took it apart. I found a blown seal, a bent spring and a cut o-ring (though the last might be my fault, I pulled it out to check and might have cut it on one of the sharp edges) I was originally going to get a Theoben gas ram to replace the bent spring but when I looked into it, it was going to be out of stock for a few months. I instead went with the E3650 which I read was a drop-in replacement. I've finally got everything I need, the spring, the o-ring, the seal (I got the tesla and the apex as I wasn't sure the difference) Now I just need to put it back together, but before I do, I have a few questions :)
I want to sand down the rough edges of the gun so I don't slice the o-ring when I put the breach back in.
What grit sand paper should I be using? (or should I use something else entirely, I do have a dremel but I'm wary about using a power tool, I don't want to over-do anything plus I don't know what attachment would be best.)
I read in the GTA Library to apply dielectric silicone grease around outside of the o-ring and the breach. That I'm pretty confident about, however I've got both moly and heavy tar, I know the heavy tar goes on the spring but I'm not sure how much to use. Where exactly does the moly go?
As for replacing the seal, I've already got the old cracked seal off, I've read a few things about putting the new one on such as heating it with a blow-drier or putting it in hot water to make it easier. Are these methods safe?
The E3650 appears to be a bit longer than the original spring, is that going to be a problem?
(https://lh3.googleusercontent.com/-_cDNGWWUmnA/TjsrIIYn6lI/AAAAAAAAA7w/PbhW8TAB3aM/s1024/IMG_20110804_192709.jpg)
There are more pictures in the other thread, or you can go to this link. https://picasaweb.google.com/106434069110082216279/CFX?authuser=0&authkey=Gv1sRgCPTC_a3rt7uYUg&feat=directlink (https://picasaweb.google.com/106434069110082216279/CFX?authuser=0&authkey=Gv1sRgCPTC_a3rt7uYUg&feat=directlink)
One final question, is there anything else I should be doing while I have my gun apart?
Thanks for any input and sorry for the huge wall of text!
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Hope This Helps. Let us know how it works out. ;D
http://www.network54.com/Forum/479035/message/1157402298/CFX+rebuild+-+long+-+pics (http://www.network54.com/Forum/479035/message/1157402298/CFX+rebuild+-+long+-+pics)
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Oh nice, I'm liking the pictures, good find, I'll defiantly use that as a reference. Thanks!
I'm still not sure how much tar / moly to use but I will poke around on the forums, I assume I don't want any globs of it left after I apply it to the spring / piston.
Hope This Helps. Let us know how it works out. ;D
http://www.network54.com/Forum/479035/message/1157402298/CFX+rebuild+-+long+-+pics (http://www.network54.com/Forum/479035/message/1157402298/CFX+rebuild+-+long+-+pics)
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Hot water with dish washing soap worked great to put on the seal. (safe to do)
Heavy tar should be used sparingly. there should not be any clumps.
Spring length. I went to Home Depot and purchased a long bolt (or wing nut) and screw (longer than the spring) with a washer on each end and let the spring set for a day; length set longer than compressed length. This makes it easier to install and just seems safer to do.
I think I used between 220 then between 320 and 360 grit
I used Charlie DaTuna's tune guide for B18 (I think it was called) and had just about everything you need to know (can't seem to find in GTA Library). Maybe someone can find the link.
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I used Charlie DaTuna's tune guide for B18 (I think it was called) and had just about everything you need to know (can't seem to find in GTA Library). Maybe someone can find the link.
I think I found it, seems to have a ton of info including most (if not all) of what I was asking, thanks for pointing me in the right direction! I will be working on this tomorrow or Sunday, I'll put any news in this thread.
http://www.charliedatuna.com/airgun_docs/B19%20Super%20Tune.doc (http://www.charliedatuna.com/airgun_docs/B19%20Super%20Tune.doc)
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Sorry for the double post, I just wanted to give an update. The gun fires :) I have no idea how well (ie if it fixed the low fps) as it's too dark out for me to use the chrony. I will pull it out tomorrow weather permitting. I'm really nervous about the seal because it was a pretty tight fit and I'm worried that it might have gotten nicked when I was putting it back in. The o-ring on the rotating breach was also tough but I think the seal was worse. If I get to shoot it tomorrow I'll post an update with some chrony numbers.
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Did you use the blue or red seal?
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Did you use the blue or red seal?
The blue one (is that the Tesla?, I think Apex was the red one), it was slightly smaller so I figured it would be an easier fit.
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Yes, that is the same one I used. the red is too tight.
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Yes, that is the same one I used. the red is too tight.
Yeah the Tesla seemed the better choice, I just hope I didn't nick the seal getting the piston installed or I'll have to take it apart and try with the Apex.
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I manged to get 4 shots over the chrony a few moments ago before the mist turned back into a steady rain. 813, 830, 830 and 820 fps with 7.9 grain Crosman hollow-points (only pellet I have to test). Success! I'm back up to about what I was shooting before the seal blew. I was hoping for a slight improvement but considering this was the first time I did anything like this I'm just glad the gun still shoots :)
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Just make sure you sand the inside really well and hone the area where the seal/piston will be moving back and forth. You can tape some tissue to a wire and run it inside up and down and feel if there are any sharp edges left that could damage the seal prior to installing it.
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Excellent! Good times (between weather) again.
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as your seal breaks in you may see a lot of veryation in fps
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Just curious, did you replace the Breech Oring and the Loading Port/ Barrel oring? If so, where did you find yours? That's where a LOT of the energy is lost in the CFX.
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I did replace the large breach o-ring as it was cut (prob when I took it out) however I didn't replace either of the 2 smaller ones (one on the breach one on the loading port) I wasn't able to find the one for the loading port, the one on the breach (the smaller one) I did find and I think i ordered one that is the right size but mine didn't appear damaged and I didn't want to mess with it. I got all my o-rings from here. www.theoringstore.com (http://www.theoringstore.com)
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Those are good fps numbers from the CFX since their not known for some higher numbers that you would see with a break barrel. The loading design of the CFX contributes to it's lower fps but the CFX has always been known for it's out of the box accuracy. I've taken my share of Bandit's with my .22 CFX. eD
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Yeah that's what I've been reading :), now I just have to wait for a sunny day so I can get the scope back on and sighted and I'll be able to shoot again, I can't wait! :)
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830 fps seems kind of slow for a .177 cal. CFX. I'm getting 750 fps with 14.3 gr. pellets from my .22 cal. CFX with a full tune (by me) with a blue tesla seal. If you can afford it, get yourself the Theoben gas spring. Good job on the rebuild.
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I have done a hundred or so of them and as Shadow said, those are about average numbers (820 to 850) for a CFX. It's not too uncommon to find them not even breaking the 800 mark. The CFX, although usually very accurate is not a powerhouse no matter what you do to them in most cases. By the same token, every once in awhile you will find an exceptional one that will get into the early 900's.
It's all in the design of the animal and one of those guns that Gene and I have discussed to great extent as well as spent a lot of time together problem solving. It came to a point, because they were so unpredictable and no matter what you did you did or no matter how much time you spent on them and not get the results expected that both Gene and I eventually decided that we would no longer tune them.
CDT
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I wouldn't part with mine. Tried one in .22 but was disappointed with it so it went back. But in .177 I really like. Accurate.
Good Luck!
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is there suppose to be a little oring in the breach and the loading port on a cfx?
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Actually very few Gamo CFX's .177 ever achieve 900 fps with 7.9 gn pellets, or above. The overall stroke is shorter due to the style of breech. Also the breech seal and o'ring inherit poor design. But if you get a good one they are dead on accurate.
830 fps seems kind of slow for a .177 cal. CFX. I'm getting 750 fps with 14.3 gr. pellets from my .22 cal. CFX with a full tune (by me) with a blue tesla seal. If you can afford it, get yourself the Theoben gas spring. Good job on the rebuild.
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Setting the spring manually is really not a good idea in most cases and isn't needed. The first time you cock the gun, let it set for about five minutes (it actually just needs a minute or two) then shoot it and it will be perfectly set for your particular action. And if setting it manually, it shound be compressed to the determined (needs to be determined by measurements) amount needed and no more. Once compressed, leave it compressed for a few minutes and then release it.
CDT